GHG Reduction

• Ways to Reduce Cement GHG at Cement Plants
  • Blending SCM at Cement Plants
  • Environmentally Friendly Fuel for Cement Kilns
  • Use of Interground Limestone
  • Production Efficiency Improvements
• Ways to Reduce Concrete GHG at Batch Plants
  • Blending SCM at Concrete Batch Plants
  • Optimize Cement Content
  • Reduce Concrete Waste
  • Universal GHG Emission Standards

Related Links

Optimizing cement content can be prescribed as a strategy to reduce GHG. In some cases, a higher amount of cement is used because of the desired early concrete strength. For instance, a homeowner or general contractor may need concrete with a compressive strength of only 2,000 psi. This 2000-psi concrete only needs about 300 pounds of cement to gain this strength at 28 days. That strength requirement can be met if the homeowner or contractor allows more time for concrete to gain strength.

Another option for homeowners and general contractors would be the use of admixtures to accelerate the strength gain of the concrete mix. While there is a cost to these admixtures, they can be used to reduce GHG through the reduction of cement. To optimize the amount of cement, concrete mixes can also reduce the amount of water used since this results in a stronger concrete. Reducing the amount of water would also involve some additional cost for plasticizer or water-reducing admixtures. This cost may be compensated for by cost savings of optimized cement content.

Example: when a mix for a concrete driveway replaces 25 percent of the cement with fly ash, and uses half the normal amount of cement, as much as 12,500 pounds of CO₂ can be saved per driveway, assuming each ton of cement emits 0.9 tons of CO₂. This is equivalent to the CO₂ emissions from about one passenger car for the entire year, as the average passenger car emits about 11,500 pounds of CO₂, based on data from the Environmental Protection Agency (EPA) (PDF 42KB). To calculate this emission, it was assumed that each car travels 12,000 miles per year, gets about 20.3 mpg (according to MOBILE 6.2, which is the EPA vehicle emission modeling software) and each gallon of fuel emits 19.4 pounds of CO₂ per gallon. To achieve this savings, it may be necessary to keep cars off of the driveway longer. If it is necessary to get strength faster so vehicles can access the driveway, these GHG savings can still be obtained by adding an accelerator to the mix at a concrete cost increase of about 10 percent. The GHG emissions and savings for different scenarios are detailed as follows:

• (20’x100’x1/2’)/27 x (600 pounds per cubic yard) ~ 20,000 pounds of CO₂
• (20’x100’x1/2’)/27 x (600 pounds per cubic yard) with 25 percent fly ash ~ 5,000 pounds savings of CO₂
• (20’x100’x1/2’)/27 x (300 pounds per cubic yard) ~ 10,000 pounds savings of CO₂ with ½ less cement
• (20’x100’x1/2’)/27 x (300 pounds per cubic yard) with 25 percent fly ash ~ 12,500 pounds savings of CO₂ with ½ less cement and 25 percent fly ash

 

 

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